a. Field of the Invention
The present invention relates to a device for automatically detecting an overload on an aerial ladder truck.
Generally, in an aerial ladder truck, the operator carefully operates the ladder so that the load will not exceed the working limit range on the basis of a working limit range diagram as shown in FIG. 1 taking into account the strengths of the ladder and other parts and the safety of the truck against toppling. Therefore, the truck is usually provided with a warning device or an automatic stopping device which operates in accordance with said working limit range diagram.
B. Description of the Prior Art
The conventional warning or automatic stopping arrangement, as shown in FIG. 2, comprises a load detecting cylinder 3 disposed adjacent the ladder support point 2 of a ladder support frame 1, a pressure switch 4 into which the pressure in the cylinder is introduced, a load detecting rod 5 which is pressed by the lower surface of a ladder 6 to detect the pressure in the cylinder, the arrangement being such that when said pressure takes a value specified by the pressure switch, a warning device or automatic stopping device (not shown) is actuated by the action of the pressure switch.
In this connection, a detection pressure to the load detecting cylinder produced by a front end load should be the same regardless of whether the ladder assumes a condition A or B shown in the diagram of FIG. 1. However, the pressure due to the self-weight of the ladder is greater in the condition B than in the condition A since the center of gravity of the ladder is located more outwardly in the condition B than in the condition A. Thus, eventually the detected pressure is greater in the condition B than in the condition A. If the detected pressure in the condition A is selected as the specified pressure of the pressure switch, then in the condition B the pressure switch reaches the specified pressure and the warning device or automatic stopping device is actuated before the working range is reached. This is due to the fact that the pressure actually detected by the load detecting cylinder differs between the conditions A and B.